1. Field of the Invention
The present invention relates generally to a lead frame for use in the manufacture of a semiconductor device, and to a method of fabricating a semiconductor device using the lead frame of the invention.
2. Description of the Prior Art
A semiconductor device, such as, for example, an integrated circuit (IC) or an LSI is fabricated as shown in FIG. 4 by properly plating a pad section 11; forming the inner tip ends of inner leads 12 of the lead frame, generally indicated by the reference character 10, by means of suitable blanking or etching operations performed upon a strip-shaped steel plate; fixedly mounting a semiconductor element, not shown, upon the pad section 11; interconnecting the terminals of the semiconductor element with the inner tip ends of the inner leads 12 by means of a suitable bonding process utilizing gold wire or the like for establishing good electrical interconnections therebetween; sealing the resultant assembly with a suitable resin; and finally severing appropriate portions of the tie bars 13, which serve to interconnect the inner and outer leads 12 and 14, respectively, by suitable trimming and forming processes.
The tie bars 13 function to stabilize the outer leads 14 of the lead frame until completion of the assembling operation, and they also serve to prevent any leakage of the sealing resin during the sealing operation of the assembly. Furthermore, the pad 11 is supported by means of a pair of support bars 16 which extend outwardly from opposite side edge portions of a frame member 15 toward opposite side edge portions of the pad 11, the pad 11, support bars 16, and frame member 15 being integrally formed together.
In fabricating the above-described semiconductor device, since the fixed mounting of the semiconductor element, not shown, upon the central pad member 11 is achieved by means of thermo-compression bonding or similar techniques, the pad member 11, as well as any other elements within the vicinity thereof, has its temperature raised to approximately 400.degree.-500.degree. C. Consequently, in view of the fact that the inner leads 12 may have, for example, their tip ends plated with a suitable metal having a relatively low melting temperature, the aforenoted technique has exhibited manufacturing defects in that the fixed mounting process achieved in connection with respect to the semiconductor element upon the central pad member 11 has simultaneously caused the undesirable melting of the plated metal upon the tip ends of the inner leads 12. Furthermore, it has also been realized that as a result of the aforenoted thermo-compression bonding or similar techniques employed in connection with the fixation of the semiconductor element upon the central pad member 11, thermal deformation of the various components, for example, the tip ends of the inner leads 12, has also occurred whereby the spacings defined between the inner leads 12 has been rendered non-uniform. This phenomenon has, in turn, present difficulties in connection with the proper and efficient performance of the aforenoted wire bonding process or technique between the terminals of the semiconductor element and the inner leads 12 of the lead frame 10.
In an attempt to rectify or overcome the aforenoted problems, it is also conventionally known and practiced to separately form or fabricate the frame member, with its inner and outer leads, and interconnecting tie bars, with respect to the pad member and its support bars. This type of prior art is exemplified by means of, for example, Japanese Patent Publication No. 60-193365 which issued to Toshinori Tanaka and was published on Oct. 1, 1985 . In such patent publication, the pad member 4 and the support bars 7 thereof have been fabricated separately and distinctly from the frame member 6 which is integrally formed with inner leads 2 and outer leads 1, as well as interconnecting tie bars 3. The pad member 4 and its support bars 7 are then subsequently affixed to the frame member portions 6 by means of welding the same thereto at connecting portions 5. Consequently, while this prior art reference teaches a fabrication technique which appears to overcome the aforenoted problem with respect to the fabrication of the entire lead frame as a single entity whereupon the deformation and melting problems are ordinarily encountered, the reference nevertheless lacks any teaching or means of resolving the problem wherein non-uniform spacing occurs or is defined between the inner leads of the lead frame, or between the inner leads and the semiconductor element disposed upon the central semiconductor pad member. In particular, while welding regions are disclosed at 5 in FIG. 2 of the Tanaka publication for welding or brazing attachment with similarly noted sections 5 of the pad member support bars 7, as shown in FIG. 3 of the Tanaka publication, there is no provision of means for precisely or accurately defining the lateral positioning of the pad member 4 and the support bars 7 relative to sections or regions 5 of the frame members 6 and along the longitudinal extent thereof, or more particularly, extending in the lateral direction, that is, left to right or right to left, as viewed in the drawing FIG. 2 of the Tanaka publication. Consequently, the disposition of the pad member 4, with its semiconductor element, not shown, disposed thereon and having terminals thereof for electrical connection with the inner leads 2 of the lead frame of Tanaka, relative to the inner leads 2, cannot be accurately or precisely achieved whereby the aforenoted wire bonding process difficulties remain unresolved.